[PATCH net] net: set fib rule refcount after malloc

[PATCH net] net: set fib rule refcount after malloc

[David Ahern]

The configure callback of fib_rules_ops can change the refcnt of a
fib rule. For instance, mlxsw takes a refcnt when adding the processing
of the rule to a work queue. Thus the rule refcnt can not be reset to
to 1 afterwards. Move the refcnt setting to after the allocation.

Fixes: 5361e209dd30 ("net: avoid one splat in fib_nl_delrule()")
Signed-off-by: David Ahern <dsahern@gmail.com>
---
 net/core/fib_rules.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index a0093e1b0235..fdcb1bcd2afa 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -400,6 +400,7 @@ int fib_nl_newrule(struct sk_buff *skb, struct nlmsghdr *nlh,
 		err = -ENOMEM;
 		goto errout;
 	}
+	refcount_set(&rule->refcnt, 1);
 	rule->fr_net = net;
 
 	rule->pref = tb[FRA_PRIORITY] ? nla_get_u32(tb[FRA_PRIORITY])
@@ -517,8 +518,6 @@ int fib_nl_newrule(struct sk_buff *skb, struct nlmsghdr *nlh,
 		last = r;
 	}
 
-	refcount_set(&rule->refcnt, 1);
-
 	if (last)
 		list_add_rcu(&rule->list, &last->list);
 	else
-- 
2.1.4

Re: [PATCH net] net: set fib rule refcount after malloc

[David Miller]

From: David Ahern <dsahern@gmail.com>
Date: Thu, 13 Jul 2017 13:36:40 -0700

> The configure callback of fib_rules_ops can change the refcnt of a
> fib rule. For instance, mlxsw takes a refcnt when adding the processing
> of the rule to a work queue. Thus the rule refcnt can not be reset to
> to 1 afterwards. Move the refcnt setting to after the allocation.
> 
> Fixes: 5361e209dd30 ("net: avoid one splat in fib_nl_delrule()")
> Signed-off-by: David Ahern <dsahern@gmail.com>

Can someone keep a scoreboard of how many bugs and arbitrary
unnecessary changes get introduced because of this new refcount_t
business rather than get fixed?

I'd really like to see how that pans out over the long term especially
with all of the backporting pain this facility is going to cause.

Anyways, David I will apply this, thanks.